Thermostatic control



June 13, 1939. BRAcE ET AL 2,162,524

THERMOSTATIC CONTROL Filed March 13, 1937 Patented June 13, 1939 UNITED STATES PATENT OFFICE THERMOSTATIC CONTROL Application March 13,

17 Claims.

The invention relates, generally, to electric arcs and more particularly, to the automatic feeding of the positive electrode in lighting devices such as searchlights in which the source of light is an 5 electric arc.

It has been the practice, in the operation of arc searchlights, to cause the positive electrode, which is consumed in the arc very rapidly compared to the rate of consumption of the-negative l electrode, to be fed-to the arc by a mechanism which is controlled by a device which is governed by the position of the arcing tip of the electrode. In such devices a thermal switch is so situated with respect to the positive arcing tip as to be l affected by the heat from the are when the tip has been consumed to such an extent as to cause the arc to be out of focus with the searchlight reflector.

The heat responsive switching devices which are employed-for positive electrode feed control are also affected by the change in the ambient temperature which varies considerably both because of the change in atmospheric temperature and because of the variation in the temperature due to heating of the searchlight by continued burning of the arc. Unless the effect of the am bient temperature change is compensated for, errors will be introduced in the operation of the searchlight which may require considerable attention of the operator in adjusting and correcting for such errors.

In the operation of searchlights as above described, the electrode is fed intermittently by the actuation of the heat responsive switch each time the electrode tip is consumed a predetermined amount. This occasions frequent oper tion of the heat responsive switch resulting in deterioration of the switch because of the excessive burden placed upon it and also resulting in a jerky op eration of the electrode feeding mechanism in feeding the electrode to bring the arc to the focus position.

It has been found that the rate of consumption of an electrode is not constant because of irregularities in the electrode material and variations in the electrode dimensions. If the electrode were consumed at a constant rate, it would only be necessary to constantly feed the electrode 50 to the are at a rate equal to its rate of consumption and the arcing tip of the electrode would remain in a fixed position.

Because of this variation in rate of electrode consumption, if it is desired to approximate a 55 constant electrode feed, it is necessary that 1937, Serial No. 130,740

means be provided for compensating for this variation.

The object of our invention is to provide a device for maintaining an arc in a predetermined position by constantly feeding the positive electrode to the arc at a predetermined adjustable rate which is approximately the slowest rate of consumption of any portion of the electrode and increasing this rate of feed when the electrode tip moves from the predetermined position a predetermined amount.

A further object of our invention is to provide a system for feeding an electrode to an are at a rate less than the rate of consumption of the arc and increasing this rate of feed when the electrode tip recedes a predetermined amount by a device which includes a heat responsive switch which comprises a single bimetallic strip so shaped as to be compensated for ambient temperature changes and which will be actuated when the electrode tip occupies a predetermined position relative thereto.

Another object of our invention is to provide a device for automatically adjusting an electrode tip to a predetermined position, the device including a means for moving the electrode to the arc and a heat responsive switch for controlling the moving means which comprises a single bi-metallic element so shaped as to respond to heat radiated upon it from the arc and to fail to respond appreciably to changes in the temperature of the atmosphere or other medium in which it is operated.

A still further object of our invention is to provide a means for steadily feeding an electrode to an arc to compensate for consumption of the electrode in the are so that the arc may be maintained at a focal point of a reflector or lens and for increasing the feeding rate when the electrode tip recedes to a predetermined point, the means for controlling the speed increasing means being a heat responsive device which comprises a single bimetallic strip so shaped as to respond inappreciably when changes of ambient temperature occur, but to respond to the radiated heat from the are when only aportion of the strip is exposed to such heat radiation, and a restricting screen for permitting the radiation from the arc to impinge upon a restricted area of the-strip only when the electrode tip has receded to the predetermined point.

Another object of our invention is to provide a heat responsive switch for controlling the electrode feeding mechanism of an electric are by so shaping a .bimetallic strip as to cause it to be responsive to heat applied on a restricted area of the strip, but not responsive to heat applied to the whole strip.

The objects of our invention are accomplished by providing the positive electrode of an arc searchlight with an electromagnetic device for automatically intermittently feeding the elec trode to the arc to compensate for .consumption of the electrode by burning in the arc and then feeding the electrode steadily continuously when the electrode tip recedes a predetermined amount from the position it is desired to have it occupy with respect to the reflector. The continuous feed is governed by a heat responsive switch which comprises a bimetallic strip bent into such a shape that, upon change of temperature of the whole strip such as would be occasioned by changes in atmospheric temperature or heating of the Searchlight due to continued use, one part of the strip will be affected to compensate for the effect on another part of the strip and the effect upon the strip as a whole will be negligible.

The heat responsive switch will respond to a temperature change of only a part of the strip since there is then no heating of the other partto cause compensation and to nullify the effect of heating of the first part. The strip is so shielded that one part of the strip only is exposed to the heat radiated from the are when the positive electrode tip recedes to where it needs readjustment. When the readjustment is made by the device, the automatic intermittent feeding of the electrode is resumed.

Other objects and advantages of the invention will be apparent from the following detailed description in connection with the accompanying drawing, in which:

Figure 1 is a diagrammatic illustration of a mechanism and system for maintaining the arcing tip of the positive electrode of an arc lamp in a predetermined position, the mechanism for manipulating the electrode being substantially the same as that shown in the copending applica-- tion of I. A. Yost and William Jacobi, Serial No. 43,372. filed October 3, 1935, now Patent No. 2,117,888, issued May 1'7, 1938;-

Fig. 2 is an enlarged elevation view of a thermostatic control device which is a part of the system shown in Fig. 1;

Fig. 3 is an elevation view of the device shown in Fig. 2 showing the form the device assumes when it is in its operative position;

Figs. 4 and 5 are front and side views of the thermostatic control device of Fig. 2 so positioned as to permit the beam from the crater of the arc to impinge on diametrically opposite sides of the thermostatic device;

Fig. 6 is an elevation View of a modification of the device shown in Fig. 2;

Fig. 7 is an elevation view of another modification of the device shown in Fig. 2;

Fig. 8 is an elevation view of still another form of the device shown in Fig. 2; and

Fig. 9 is an illustration of a section of the thermostatic devices shown in Figs. 1 to 7, taken along a line such as IXIX of Fig. 2, illustrating the manner in which these devices may be shaped to provide snap action.

Referring to Fig. 1, the reference character 10 denotes the supporting structure for the positive and negative electrodes Ii and 12 of an arc searchlight or any device in which an arc is the source of illumination and in which it is desired to maintain an arc at a predetermined position such, for instance, as at the focus of the reflector (not shown) used to project the light from the arc. A mechanism 13 is provided for continuously'feeding the electrode to the are at a rate which is equal or slightly less than the ratev of consumption in the arc.

The device l3rcomprises a continuously driven motor 14 whose field excitation may be varied by resistance 15 to adjust the motor speed. Motor i4 drives the head 16 through gearing l1 and sleeve 18 tocontinuously rotate the positive electrode I I around its own axis. 7

Connected with gear I1 and, therefore, driven thereby is a cam member 19 whichintermittently and regularly raises the one end of the arm 20 against the bias of spring 21 causing the detent 22, which is carried by the arm 20, to engage the gear 23.

Gears 23 and 24 are free to rotate upon the sleeve I8 and are normally made to rotate with the head l5 by virtue of the meshing of gear 25 with gear 24.

Gear 25 is connected by a shaft to worm gear 26 which when it is rotated cooperates with worm wheel 21 to drive a feeding wheel (not shown). which is mounted on the same shaft as wheel 21 for urging the positive carbon toward the arc. Gears 25 and 26 are carried by a sleeve 28 which is secured to or integral with head 16.

Normally there is no relative motion between gears 24 and 25, but when the cam I9 causes the detent 22 of arm 20 to engage the floating gear 23, the rotation of gears 23 and is stopped, and since the mounting for gear 25 continues to rotate with head I6, rotation of gear 25 about its own axis will take place and this will cause the worm gear 26 to rotate its worm wheel 21 which in turn will cause the feeding wheel to urge the positive electrode forward.

The speed of the motor 14 is so regulated as to cause this feeding mechanism to urge the electrode ll toward the are at approximately the rate of consumption of the electrode in the arc. However, due to irregularities in the electrode both in material composition and dimensions, it may happen that the electrode will burn at a more rapid rate than that at which it is being fed to the arc and this will cause the arcing tip to recede. It is then necessary to provide an additional means for moving the electrode tip back to the desired position.

The adjusting movement of the arc is accomplished by a mechanism which comprises a lens 29 so positioned as to concentrate rays from the arc tip through the opening 30 upon the thermal responsive device 3| when the arc tip has receded a predetermined distance from its normal position. The position a represents the normal position of the arcing tip of thepositive electrode, and the position b represents roughly the position of the are when it has receded to such a position as to require adjustment back to the normal position. When the arc tip has moved to position 1), its rays will be concentrated upon the thermostatic element 3| by lens 29 causing thermostatic element 3! to close contacts 32 to complete a circuit through the electromagnetic device 33.

When the electromagnetic device 33 is energized, it moves pin 34 into engagement with gear 23 to cause the arc feeding mechanism to move the electrode toward the arc in the same manner as was explained hereinbefore in connection with the functioning of the detent 22.

The movement of the electrode will continue so long as pin 34 engages gear 23, and this engagement will take place so long as the arcing tip of the electrode is in a position to affect the thermostatic element 3|. As soon as the arcing tip has moved to position a, thermostatic element 3! will no longer be afieeted by the heat rays from the arcing tip and will open contact elements 32 to cause the release of the pin 34 from the gear 23.

The are feeding mechanism, as driven by the motor l4 and cam member 19, will now continue to feed the electrode to the are at the predetermined constant rate determined by the speed of the motor l4 until such condition occurs which causes the arcing tip of the electrode II to recede from the normal position a to the position b.

In order to secure uniform operation of the thermostatic switch device, it is necessary that the thermostatic device be so constructed that variations in ambient temperature, which may be caused by variations in atmospheric temperature and also the variation in the temperature of the searehlight from cold to full running condition, will not cause an appreciable relative movement of contact elements 32. The thermostat shown more in detail in Figs. 2 through 5 has been especially designed for this purpose.

Referring to Fig. 2, thermostatic device 3| is shown as made up of a single strip of bimetallic material bent into circular form and having its two ends fastened to the mounting block 35. In the form shown, the metal having the higher coefficient of thermal expansion is on the inner side of the ring and the metal having the lower coeiilcient of thermal expansion is on the outside of the ring.

It will be seen that the diameter of a ring so constructed of a single strip'of bimetallic material will vary only a small amount with changes in ambient temperature, and for this reason changes in ambient temperature will cause very little relative movement of the contact elements When the beam from the arc tip is impinged upon a very limited portion of this ring, however, the greater expansion of the inner ring at this point will cause the ring to assume the shape shown in the solid lines of Fig. 3, and will cause contact elements 32 to engage each other to close the circuit shown in Fig. 1. The dotted line in Fig. 3 shows the normal position of the ring 3| when the rays from the are tip are shielded from it by plate 36.

The ring may be made of a single strip with its two ends secured against relative movement as described, or it may be made of a single continuous strip of bimetallic material. The essential feature is that the ring be substantially closed.

In Figs. 4 and 5, we have shown the ring 3| so situated with respect to the opening 30 in the shield 36 as to permit the heat rays from. the arc tip to impinge upon two diametrically opposite portions of the ring. With the ring in this position, it will cause contact elements 32 to move to circuit closing position more quickly than when 'the heat rays are concentrated upon a single portion of the ring. The action of the heat on the ring, however, will be the same as that described in connection with Figs. 2 and 3.

fixed support 33 and the strip is bent into approximately a circle with the strip slightly longer than the circumference of the circle and with the other end 39 of the strip somewhat overlapping the end 31.

It will be seen that changes in ambient temperature and, therefore, the change of the temperature of the entire bimetallic strip will not cause movement of contact element 40 toward contact element 4| for the reason that any tendency to increase the diameter of the circle between the end 39 and the point 42 will be compensated for by a similar increase in diameter between the points 31 and 42, and the net result will merely be a sliding movement of end 39 upon end 31. However, when the concentrated rays from the aretip impinge upon a limited portion of the ring through the opening 30, the portion of the circle between the points 42 and 39 will act as though it were secured at point 42, and there will be such a distortion of this portion of the ring as to cause contact element 40 to move toward contact element 4i.

In the modification of 7. we have shown a bimetallic strip bent into an S-shape and carrying a contact element 43 at one end and having its other end secured to a fixed support. In this form of the thermostatic device, the metal of the lower coeificient of thermal expansion will be on the top side of the strip, as shown in the figure, and the metal of the higher coefficient of expansion will be on the bottom side. It will be seen that increase in ambient temperature will cause point 44 to move toward point 45, and also that this change in ambient temperature will, at the same time, cause point 46 to move away from point 44. These two movements being in opposite directions will neutralize each other, and there will be no relative movement between the contact elements 43 and 4?. Concentration of the heat rays from thebeam on the strip, however, will cause a heating of only a portion of the strip, as shown by the relative position of the strip and the opening 30 in the diagram, and will cause contact element 43 to move toward contact element 41 to complete the control circuit.

Contact elements 5| and 52 may be provided to be controlled by the form of thermostatic device shown in Fig. 7, if it should be desirable to control a circuit by concentration of heat on the device between points 44 and 45. If it should be desirable to control a circuit by back contacts on this device, these contacts may be provided so disposed as to be in circuit closing position when the device is in normal position.

We have shown in Fig. 8 a modification of the device shown in Fig, 2 to show that it is only necessary that the single strip be formed into a body of such shape that the change in the ambient temperature will cause compensating movements of the different parts of the body, but that concentration of heat on any particular portion of the body will distort the body. The device shown in Fig. 8 is in the form of a triangle, shaped from a single bimetallic strip, having one corner secured to a stationary support and having a contact element 49 secured to another corner, with the side of the triangle between the support and the contact element so situated with respect to the opening 30 as to allow the heat rays from the are tip to impinge upon this side of the triangle when the are tip has receded from its desired position.

In this form of the invention, changes in ambient temperature will cause a slight bending of each of the sides of the triangle, but when heat is concentrated upon the side 53, the triangle will be so distorted as to cause contact elements 49 and to engage and complete the control circuit. In this form of the invention also, the metal having the higher coefficient of thermal expansion is situated on the inside of the triangle.

In order to provide snap action for the thermostatic switching device, the bimetallic strip may be shaped as indicated in Fig. 9, which is an enlarged. section of the circular strip taken along the line IX-IX of Fig. 2. With the bimetallic strip shaped as shown after a slight bending of the side which is being affected by the heat concentration, the strip will snap to the distorted circuit closing position. I

In this form the bimetallic strip is so shaped as to cause it to pass from the form shown in solid lines in Fig. 9 through an unstable condition shown in broken lines at A to the form shown in broken lines at B. In passing from position A to position B, a snap action occurs which suddenly accentuates the elongation of the side of the ring under the heating influence of the beam from the arcing tip of the positive electrode and causes contact elements 32 to close very quickly. It is to be particularly noted that this snap action is accentuated by the tendency of the bimetallic element to decrease the curvature of the section shown in Fig. 9 when this portion of the ring is exposed to the heat rays from the arcing tip. The bimetallic element in any of the forms of the invention shown may be shaped in this manner for snap action. The dimensions of the section shown in Fig. 9 are merely illustrative of the general shape of the device and are not to be taken as showing the actual or relative dimensions of the bimetallic strip.

It will be seen that we have invented a device which is simple and inexpensive to manufacture and which will operate to feed an electrode to an arc continuously at a rate which is equal to or slightly less than the rate of consumption of the electrode, and for increasing this rate of feed when the electrode tip recedes from a predetermined position a predetermined amount, and for providing a control device which includes a heat responsive switch comprising a single bimetallic strip so constructed as to be compensated for ambient temperature changes, and which will be actuated when the electrode tip occupies a predetermined position relative thereto.

.In compliance with the requirements of the patent statutes, We have shown and described herein the preferred embodiments of our invention. It is understood, however, that the invention is not limited to the precise construction shown and described, but is capable of modification by one skilled in the art, the embodiments herein shown being merely illustrative of the principles of our invention.

' We claim as our invention:

1. In an electrode feeding mechanism for electric arcs, in combination, means for feeding the electrode, and means including only one strip of bimetall c material so shaped as to be appreciably responsive to temperature change only when the change is effected in limited parts of the strip, responsive to the position of the arc, for controlling the electrode feeding means.

2. In an arc searchlight, means for feeding an electrode to compensate for consumption of the electrode in the arc, said means comprising a mechanism for feeding the electrode at. a substantially constant rate, only one bimetallic element so formed as to be appreciably responsive to temperature change only when such change is effected in limited parts of the element, means governed by the position of the electrode tip for causing the radiated heat from the arc to impinge upon a limited portion of the element, and means whereby the response of the element to temperature increase at such limited portion causes a change in the feeding rate of the electrode.

3. In an arc searchlight having a reflector, means for feeding an electrode of the searchlight to compensate for consumption of the electrode in the are so that the tip of the electrode may be maintained at the focus of the searchlight reflector, only one bimetallic member so formed as to be appreciably responsive to temperature change only when such change is effected in limited parts of the element, means governed by the position of the electrode tip for causing the radiated heat from the arc to impinge upon a limited portionof' the member, and means whereby response of the member to temperature increase at such limited portion causes movement of the electrode.

4. In a device for controlling the feed of an electrode to an arc, only one bimetallic member so formed as to be appreciably responsive to temperature changeonly when such change is effected in a limited portion of the member.

5. In a device for controlling the feed of an electrode to an are, only one thermal responsive member so formed as to respond appreciably to temperature change only when such change is effected on a limited portion of the member.

6. In a device for controlling the feed of an electrode of an arc searchlight to compensate for consumption of the electrode in the are so that the arc may be maintained at the focus of the searchlight reflector, only one thermal responsive member so formed as to respondappreciably to temperature change only when such change is effected on a limited portion of the member, means governed by the position of the electrode tip for causing, the radiated heat from the arc to impinge upon a limited portion of said memher, and means whereby response of the member to temperature increase at such limited portion causes movement of the electrode.

7. In a system for controlling the feed of an electrode of an arc searchlight to compensate for consumption of the electrode in the are so that the arc may be maintained at the focus of the searchlight reflector, a thermostatically responsive device comprising a substantially circular endless band of bimetallic strip, means governed by the position of the electrode tip for causing the radiated heat from the arc to impinge upon a limited portion of the band, and means whereby the deformation of the band due to temperature increase at the limited portion thereof causes movement of the electrode.

8. In a system for controlling the feed of an electrode of an arc searchlight to compensate for consumption of the electrode in the arc so that the arc may be maintained at the focus of the searchlight reflector, a thermostaticall responsive device comprising a bimetallic strip formed in substantially an S-shape, means governed by the position of the electrode arcing tip for causing the radiated heat from the arc to impinge upon a limited portion of the strip, and means whereby the deformation of the strip due to temperature increase at the limited portion thereof causes movement of the electrode.

- comprising a bimetallic strip formed in substantially an S-shape and means holding one end 9.Ina-deviceioroontmllingtheleedo!an electrode to an arc. a thermostatically responsive device comprising a bimetallic strip formed in substantially an S-shape and means holding one end of the S-shaped strip in a ilxed position.

10. In a device for controlling the feed of an electrode to an are. a switch operating device of the S-shaped strip in fixed position.

li..In a system for controlling the feed or an electrode an arc searchlight to compensate ior consumption of the electrode in the are so thatthearcmaybemaintainedattheiocus oi the searchlight reflector, a thermostatically responsive device comprising a bimetallic strip formed in a substantially circular band with one end 0! the strip overlapping and slidably bearing upon the other end, means governed by the position of the electrode arcing tip for causing the radiated heat from the arc to impinge upon a limited portion 0! the strip, and means whereby deformation of the strip due to temperature increase atthe limited portion thereol causes movement of the electrode.

12. In a device'i'or controlling the feed of an electrode to an are, a thermostatically responsive device comprising a bimetallic strip formed in a substantially circular band with one end of the strip overlapping and slldably bearing upon the other end.

13. In a device for controlling the feed of an electrode to an arc, a switch operating device comprising a' bimetallic strip formed in a substantlally circular band with one end of the strip overlapping and slidably bearing upon the other end.

14. In a system for controlling the feed of an electrode of an arc searchlight to compensate for consumption of the electrode in the are so that the arc may be maintained at the locus of the searchlight reflector, means including only one bimetallic strip so shaped as to be appreciably responsive to temperature change onLv when the change is elected in a limited portion oi the strip, the strip being so formed as to produce a snap action when responding to the temperature change, means governed by the position oi the electrode tip for causing the radiated heat from the arc to impinge upon a limited portion 0! the member, and means whereby response of the member to temperature increase at such limited portion causes movement of the electrode.

15. In a device for controlling the teed of an electrode to an are, a switching device comprising only one bimetallic member so formed as to be appreciably responsive to temperature change only when such change is eil'ected in a limited portion of the member and so formed as to produce a snap action 01 the switch when responding to the temperature change.

16. In a system for controlling the ieed of an electrode 01' an arc searchlight to compensate for consumption of the'electrode in the are so that the arc may be maintained at the focus of the ends held against movement relative to each other. I

PORTER H. BRACI. CLINTON R. HANNA. KIRK A. OPLINGIR. 

